1. Field of the Invention
The present invention relates to an armature winding structure for use in an electric motor.
2. Description of the Prior Art
One conventional winding structure for use on the armature of an electric motor is shown in FIG. 22 of the accompanying drawings.
The winding structure comprises a winding D generally known as a helical winding. The winding D is composed of three parallel web-shaped strand bundles 50, 51, 52 each comprising a plurality of parallel strands, the strand bundles 50, 51, 52 being allotted respectively to U-, V-, and W-phase currents. The strand bundles 50, 51, 52 are folded over on themselves at certain intervals into a flat configuration. The folded flat winding structure has a plurality of folded edges 53, 54 on its opposite sides and a plurality of straight conducting regions 55, extending between the folded edges 53, 54, where currents flow in a straight direction. These straight conducting regions 55 are disposed adjacent to one another, and jointly make up a flat strand plate 56 in which the strand bundles 50, 51, 52 extend transversely. Since the winding D can easily be manufactured, it is widely used as armature windings.
In the U-phase, however, the folded strand bundle 50 overlaps itself in each of folds e at the folded edges 53, 54. The overlapping strand bundle 50 causes the current to flow in opposite directions through the face and back areas of each fold e. Since the magnetic fields generated by the current flowing in the opposite directions cancel out each other in each fold e, the winding D brings about a loss when used as a motor armature winding. In view of the fact that the currents of one set of phases, such as V- and W-phases, among the U-, V-, and W-phases, flow in one direction, the strand bundles 51, 52 for the V- and W-phases as well as the strand bundle 50 for the U-phase also overlap themselves at the folded edges 53, 54, as shown hatched in FIG. 22. The overlapping regions of these strand bundles 50, 51, 52 total 33 through 56% of the entire area of the flat strand plate 56. Therefore, the winding D is responsible for a very large torque loss.
With the overlapping strand bundles 50, 51, 52, the winding D as it is incorporated in an electric motor requires a relatively large number of strands in order to produce a desired torque. Therefore, the winding D is relatively heavy, and so is the electric motor. In the electric motor, the winding D is positioned between a core and a rotor. Inasmuch as the winding D is rendered thick by the overlapping strand bundles 50, 51, 52, the core and the rotor are spaced from each other by a large distance, and the flux density between the core and the rotor is relatively low, also resulting in a torque loss.
Furthermore, the directions in which the currents flow through the strand bundles 50, 51, 52 extend obliquely to the axis of the electric motor. Consequently, the magnetic field generated by the winding D and the magnetic field generated by a magnet (not shown) have different directions. As a consequence, the electric motor produces electromagnetic forces with low efficiency, causing a torque loss.